Isothermal Crystallization Behavior Research Articles

Composition design and crystallization behavior of Zr–Cu–Ni–Al bulk metallic glasses

The Zr–Cu–Ni–Al system was explored in this study, and seven new compositions of Zr-based bulk metallic glasses (BMGs) were designed by combining different proportions of binary eutectic phases Zr38Cu62, Zr76Ni24 and Zr51Al49, and rod-like shape samples were prepared with different diameters using the copper mold casting method. Modifying the proportion coefficient of these eutectic units, the width of the supercooled liquid region was increased from 79 to 95 K, and the thermal stability of the prepared metallic glass was improved. Differential scanning calorimetry was used to investigate the non-isothermal and isothermal crystallization behavior of the prepared samples. Noticeably, there was a small low-temperature exothermic peak before the glass transition temperature Tg in the non-isothermal crystallization process, which was related to the structural relaxation. The crystallization transition activation energy fitted by the Kissinger equation had the same variation trend as that obtained by the Arrhenius equation. Among the four metallic glasses studied, the glassy phase of Zr55·5Cu23·25Ni9Al12.25 was more stable, showing higher glass transition activation energy and longer incubation time. In addition, the isothermal crystallization processes of four metallic glasses were studied according to the Johnson-Mehl-Avrami (JMA) model. The calculated average Avrami exponents were >2.5, indicating that the nucleation rate increased during the isothermal crystallization process.

Analyzing isothermal crystallization of poly(lactic acid)/polyol systems: Correlated DSC and simulation studies

The isothermal crystallization behavior and kinetics of poly(l-lactic acid) (PLLA) melt-blended small amounts (0.7%–1%) of polyols (D-mannitol, D-sorbitol, and xylitol) were investigated by differential scanning calorimetry (DSC), and the interaction between polyols and PLLA was clarified via multiscale theoretical simulations. The decreased peak crystallization time and full width at half peak maximum (FWHM) of polyol-modified PLLA indicates that the crystallization capability of PLLA was improved, and the process was accelerated. The crystallinity remains unchanged before and after modification at the same temperature. The Avrami exponent (n) is largely unaffected, indicating that polyols as nucleation accelerants hardly alter the nucleation and growth mechanisms of PLLA crystallization. The outputs of long-term molecular dynamics simulations were fulfilled toward large-scale periodic models for three polyol-PLLA models that involved over 20,000 atoms. Therein, the interaction energies and the derived radial distribution function (RDF) implied the hydrogen bonding occurred between polyol and PLLA. To visualize the interaction sites between the polyol and PLLA, the frontier orbital distributions of the polyols were further calculated according to density functional theory (DFT). Theoretical evidence suggests that polyols improve the crystallization capability of PLLA by hydrogen bonding between the terminal hydroxyl group and the carbonyl oxygen of PLLA.

Thermal and structural behavior of mango (Mangifera indica L) kernel fat from three Ivorian varieties

AbstractMango (Mangifera indica L.) seeds is an interesting source of fat, rich in stearic (St) and oleic (O) acid with three major triacylglycerols (TAG): StOSt, StOO, and StLSt. The kernel fat content and quality depend however on the varieties and their origin. The objective of this study was to investigate the crystallization and polymorphic behavior of mango kernel fat extracted from three selected Ivorian varieties which differ in terms of TAG composition: Kent (KT), Djakoumankoun (DN) and Brooks (BR). The isothermal crystallization behavior was examined at 15 and 20°C by pulsed nuclear magnetic resonance, differential scanning calorimetry, x‐ray diffraction (XRD) and polarized light microscope. Under static conditions, DN crystallized faster, followed by BR, then KT. At 15°C, an unusual evolution was observed for both DN and BR, which can be explained by a melt‐mediated polymorphic transition from α into more stable forms. Using a differential scanning calorimetry (DSC) stop‐and‐return technique, different crystallization behaviors were also observed. Isothermal XRD experiments confirmed that the kinetics of the polymorphic transformation was different within the three samples, even if the three fats were β‐3L‐tending. At 15°C, KT transformed from liquid state to stable form without passing through α‐form, while DN and BR crystallized first into α‐from which transformed further to β′, then into stable β‐form. At 20°C, DN and BR crystallized directly from liquid to β′, which later transformed into β‐form while KT did not crystallize under the same conditions. The huge differences observed result from the differences in the TAG profiles, mainly in the StOO and StOSt content.

Effects of organic modified hectorite on performance, isothermal crystallization behavior and interface interaction of poly(lactic acid) film

In this work, in order to improve the properties of PLA, Hec-g@OA/PLA nanocomposite films were prepared by a single-screw extrusion film blown machine with PLA as a matrix and organically modified hectorite (Hec-g@OA) as a filler, and the optimum filler mass ratio of Hec-g@OA was preferred as an objective function of mechanical properties. The mechanical properties of PLA were found to increase from 24.31% to 61.75% when the mass percentage of Hec-g@OA was 0.3 wt%. Secondly, isothermal crystallization behavior of the nanocomposite films was analyzed by simultaneous rheology and FTIR technology for the purpose of further studied the effect of Hec-g@OA on the isothermal crystallization behavior of PLA, which showed that the half-crystallization time of Hec-g@OA/PLA decreased from 7.01 min, 28.99 min and 77.88 min to 3.87 min, 20.59 min and 65.78 min, respectively, at 130 °C, 135 °C and 140 °C. Finally, the form of the interaction between PLA and Hec-g@OA was analysis by electronic structure calculations and energy decomposition, it was analyzed that electrostatic interaction was found to be the main impact factor for induced crystallization of Hec-g@OA/PLA nanocomposite films, while induction and dispersion were found to be the minor impact factors.

Isothermal crystallization behavior of poly-ether-ether-ketone/bioactive glass composites and its correlation with scaffold warpage in laser powder bed fusion process

The preparation of poly-ether-ether-ketone/bioactive glass (PEEK/BG) composite scaffolds using laser powder bed fusion (LPBF) has enormous clinical potential. However, ensuring the desired accuracy and reproducibility of composite scaffolds during the LPBF process remains a significant challenge. Therefore, a thorough understanding of the relationship between the crystallization behaviors and the scaffold warpage during the LPBF process is crucial. To address this challenge, this study systematically investigates the isothermal crystallization kinetics of PEEK/BG composites and their relationship with scaffold warpage. The results reveal that the crystallization rates of pure PEEK and PEEK/BG composites decrease as isothermal crystallization temperature increases. Additionally, BG significantly suppresses the isothermal crystallization kinetics of PEEK, resulting in a 250% increase in the half-crystallization time (t1/2) of PEEK/25 wt% BG at 316 °C relative to pure PEEK. Extrapolating the t1/2 using the Hoffman-Lauritzen model can obtain the optimal powder bed temperature (Tb) for each powder in LPBF. Pure PEEK and PEEK/25 wt% BG Diamond scaffolds are printed at the respective inferred Tb (330 °C and 323 °C) and their warpage degrees are compared to that of the pure PEEK scaffold printed at 323 °C. The results demonstrate that raising Tb from 323 °C to 330 °C and adding 25 wt% BG are both effective methods to reduce the scaffold warpage by slowing down the crystallization kinetics of PEEK, resulting in reductions of 57.8% and 50.6% in warpage degree respectively. Furthermore, the incorporation of BG successfully tackles the challenge of simultaneously preventing warpage and secondary sintering in pure PEEK printing. Overall, this study offers a deep comprehension regarding the relationship between crystallization kinetics and scaffold warpage, which is crucial for achieving the reproducibility with desired accuracy of LPBF-printed biological scaffolds for clinical applications.

Non-Isothermal Crystallization Kinetics of Montmorillonite/Polyamide 610 Nanocomposites.

Non-isothermal crystallization kinetics of montmorillonite (MMT)/polyamide 610 (PA610) composites were readily prepared by in situ melt polymerization followed by a full investigation in terms of their microstructure, performance, and crystallization kinetics. The kinetic models of Jeziorny, Ozawa, and Mo were used in turn to fit the experimental data, in all of which Mo's analytical method was found to be the best model for the kinetic data. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) studies were used to investigate the isothermal crystallization behavior and MMT dispersion levels in the MMT/PA610 composites. The experiment results revealed that low MMT content can promote the PA610 crystallization, whilst high MMT content result in MMT agglomeration, and reduce the PA610 crystallization rate.

Control of the crystalline morphology of polyphenylene sulfide in secondary thermoforming by the strong memory effect of crystallization

Polyphenylene sulfide (PPS), as a typical resin for aerospace thermoplastic composites, often undergoes repeated melting and crystallization during thermoforming. Thermal histories can introduce the self-nucleation (SN) effect in certain circumstances, which will significantly accelerate the overall crystallization rate of PPS. In this article, the SN behavior of PPS and its influence on nonisothermal and isothermal crystallization behavior were studied by differential scanning calorimetry, and the multiscale crystalline morphology and structure were characterized. A unique SN domain within the temperature range of 292 °C–323 °C was identified, where the melting endotherm reaches the melt baseline and the peak crystallization temperature remains stable, while the spherulite size is several hundred nanometers. The mechanisms of the impact of molecular chain topology at different melting temperatures on the SN behavior were proposed. This work provides guidance for the design of PPS crystalline structure and suggests a stable thermoforming processing region, approximately 20 °C above the melting point.

Prediction of Unwanted Crystallization of Freeze-Dried Protein Formulations Using α-Relaxation Measurements.

There is a lack of methods to predict the isothermal crystallization behavior of amorphous freeze-dried formulations stored below the glass transition temperature. This study applies isothermal microcalorimetry to predict long-term crystallization during product storage time. The relaxation curve of a fresh sample recorded within 12 h after lyophilization is correlated with the long-term crystallization time at the same temperature. Storage conditions of 25 °C and 40 °C are examined and five model formulations containing either sucrose or trehalose with different concentrations of an IgG1 antibody are investigated. The amorphous formulations were created by different freeze-drying processes only differing in their freezing step (random nucleation; additional annealing step of 1.5 h and 3 h, controlled nucleation; quench cooling). Samples that crystallized during the study time of 12 months showed a promising correlation between their relaxation time and crystallization behavior upon storage. Furthermore, the study shows that polysorbate 20 strongly accelerates crystallization of sucrose and that the freezing step itself has a strong impact on the relaxation phenomena that is not levelled out by primary and secondary drying.

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage.

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0-100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass-crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.

Liquid Metal as a Liquid State Nucleating Agent for Poly(l‐lactide)

AbstractThis work for the first time reports that liquid metal (LM, gallium) behaves as a nucleating agent for the plastic poly(l‐lactide) (PLLA). The LM‐PLLA composites with different content (0–10%, by weight) of LM are fabricated by a twin crew extruder. The impacts of LM content on non‐isothermal and isothermal crystallization behavior are systematically investigated by calorimetry combing with Avrami's theory, determining an optimal LM content (2.5%) for advancing the crystallization of PLLA. Wide‐angle X‐ray diffraction (WAXD) shows that the excessive LM will interfere with the crystal structure of X%LM‐PLLA. As a kind of liquid state nucleating agent in plastic, the nucleation mechanism of LM for PLLA is attributed to the production of carboxylate ion clusters from the reaction between carboxylic acid on the end group of the PLLA chain and gallium, which is distinct from the epitaxy mechanism of previous solid nucleating agents.

Magnetic properties evolution and crystallization behaviour of vacuum- and air-long-term-annealed rapidly quenched Fe80.3Co5Cu0.7B14 alloy

This work aims to investigate the isothermal crystallization behaviour, crystal structure and magnetic properties evolution of long-term (up to 300h) low temperature (210 and 260°C) vacuum- and air-annealed Fe80.3Co5Cu0.7B14alloy. Before the α-Fe(Co) phase crystallization, the primary relaxation process has been identified at a temperature range up to 340°C. The relaxation process performed under 210°C for 300h did not initiate the crystallization process. However, the topological and compositional short-range rearrangements improved magnetic properties remarkably. Annealing 150h at 260°C helps to deliver enough energy to stabilize the glassy state and initiate the crystallization process fully. Structural and magnetic properties evolution of 150h annealing at 260°C corresponds to the evolution presented during isochronal 20min annealing at 310°C. Magnetic properties Bs = 1.75-1.79T, Hc < 20 A/m and P10/50are similar to those for 20min of annealing at 310°C. Comparison of core power losses from up to 400kHz frequency dependences of long-term low temperature annealed alloy with 20min classical annealing at 310°C shown that presented here long-term annealing is energetically insufficient to bring the glassy state system into the same low level of core power losses efficiency.

Role of the Branched PEG-b-PLLA Block Chain in Stereocomplex Crystallization and Crystallization Kinetics for PDLA/MPEG-b-PLLA-g-glucose Blends with Different Architectures.

The isothermal crystallization behavior and corresponding morphology evolution of poly(d-lactic acid) (PDLA) blends with PLLA6.7k or MPEG-b-PLLA6.7k-g-glucose with different architectures and different PLLA-grafted copolymer contents were investigated. The formation of stereocomplexes (SCs) in between the chain branched structure of MPEG-b-PLLA6.7k-g-glucose and PDLA chains acting as the physical crosslinking points slows down the motion of PDLA chains, but the SCs could act as a heterogeneous nucleating agent for the late formation of homocrystals (HCs) in the blend system, accelerating the crystallization kinetics of HCs through enhancing the nucleation density. For PDLA/MPEG-b-PLLA6.7k-g-glucose blends, the mobility of SCs in the blend system and the nucleation density of SCs in the blends exhibit oppositional behavior during the isothermal crystallization at a Tc of 130 °C. The evolution of the crystal growth and structure during the isothermal crystallization process by rheometry has revealed the interesting role of the branched chains of MPEG-b-PLLA6.7k-g-glucose in the mechanism of the crystallization in PDLA blends.

Confocal scanning laser microscopy investigation of crystallization behavior of hot blast furnace slag

The isothermal and non-isothermal crystallization behavior of blast furnace (BF) slag with varying CaO/SiO2 ratios was in-situ observed through a confocal scanning laser microscopy (CLSM). The crystallization kinetics was analyzed and precipitation of crystalline phases was discussed by theoretical analysis from FactSage 8.0 and X-ray Diffraction (XRD). The results showed that, with the increasing CaO/SiO2 ratio from 1.0 to 1.3, the crystals morphology changed first from rectangles and squares to small-size and irregular, and further to long strip shape at the cooling rate of 100 °C/min. The onset crystallization temperature in CTT diagram was higher at a larger CaO/SiO2 ratio due to the decrease of polymerization degree of the slag. For the isothermal crystallization process at 1250°C, the crystals morphology changed gradually from lamellar to long-trip or columnar, and the incubation period in TTT diagram became shorter with the increase of CaO/SiO2 ratio. Avrami index n decreased from appropriately 2.3 to 1.5, and the growth mode of crystals converted from two-dimensional to one- dimensional. XRD analysis showed that only merwinite existed in four slags at 1380°C. Akermanite and gehlenite were generated at 1350°C, and their amount first increased greatly and then decreased slightly with a continuous increase of CaO/SiO2 ratio. At the low temperature, the number of akermanite and gehlenite reduced, while that of merwinite increased obviously in the slags when CaO/SiO2 ratio was 1.2 and 1.3, indicating that increasing CaO/SiO2 ratio promoted the generation of merwinite.

Effect of Interphase Properties on Isothermal and Non-isothermal Crystallization Behavior of Poly(lactic acid)/Acetylated Starch Blends.

The effect of interphase properties on the crystallization behavior of blends of poly(lactic acid) (PLA)/acetylated starch (AS) with different degrees of substitution (DSs) was investigated. Under isothermal crystallization conditions, the rate of crystallization was higher for PLA/DS0.5 and lower for PLA/DS1.5 and PLA/DS2.5 when compared to PLA. In contrast, non-isothermal crystallization behavior indicated a slower rate of crystallization of PLA/DS0.5 and a faster rate of crystallization of PLA/DS1.5 and PLA/DS2.5 compared to PLA at the highest cooling rate (5 °C/min). The potential relationship between crystallization behavior and interphase properties and interphase thickness and formation of rigid amorphous fraction in the interphase, was investigated. The formation of a rigid amorphous fraction in PLA/DS1.5 and a thick interphase in PLA/DS2.5 prevented the formation of crystals on the dispersed phase and interrupted the crystallization under isothermal conditions. Hydrogen bonding in the PLA/DS1.5 blend and hydrophobic interactions in the PLA/DS2.5 blend may facilitate the crystallization at high cooling rates under non-isothermal conditions. Small-angle X-ray scattering analysis revealed the presence of a smaller lamellar structure in PLA/AS blends. The largest amorphous phase among blends was observed for the PLA/DS1.5 blend, which can be attributed to the hydrogen bonding in the interphase region of this blend.

Enhancement of the properties of poly(L-lactide)/poly(butylene adipate-co-terephthalate) blends by introduction of stereocomplex polylactide crystallites

Herein, poly(L-lactide) (PLLA), poly(butylene adipate-co-terephthalate) (PBAT), and poly(D-lactide) (PDLA) were melt compounded by a low-temperature method to prepare ternary blends with balanced properties. Differential scanning calorimetry results and torque changes during melt blending confirmed that the stereocomplex polylactide (SC-PLA) crystallites were formed. Network structure composed of SC-PLA crystallites was formed when the PDLA content was 5 wt%, at which point the melts of the blend exhibited solid-like rheological behavior. The formation of SC-PLA crystallites increased the viscosity ratio between PLLA and PBAT melt, which led to an increase of the size of dispersed PBAT phase. Furthermore, the SC-PLA crystallites could greatly promote both nonisothermal and isothermal melt crystallization behaviors of PLLA/PBAT/PDLA ternary blends because of their effective heterogeneous nucleation effect. The ternary blend containing 2 wt% PDLA showed good toughness and had an elongation at break of 211% compared to the elongation at break of 3.5% for neat PLLA. These biodegradable blends showed excellent melt crystallization abilities as well as tailored rheological and mechanical properties, which could demonstrate their potential as traditional non-biodegradable plastic substitutes.

Crystallization kinetics of Cu50Zr40Ti10 amorphous powder

The non-isothermal and isothermal crystallization behaviors are systematically investigated for the gas-atomized and as-milled amorphous alloy powders. The results show that the crystallization phase is Cu10Zr7 phase for the gas-atomized and as-milled amorphous alloy powders in non-isothermal and isothermal crystallization modes. The glass transition temperature, onset crystallization temperature, and crystallization peak temperature are larger for the as-atomized alloy powders than for the as-milled ones. The activation energies for the glass transition and crystallization are lower for the as-atomized alloy powders than for the as-milled ones. The crystallization mechanism of the gas-atomized and as-milled amorphous alloy powders nearly depends on the heating rates and the annealing temperatures. The detailed crystallization mechanism of non-isothermal and isothermal modes are discussed.

Role of long-chain backbone in side-chain crystallization of densely grafted comb-like polymers

Crystallization behaviors of alkane side-chains in densely grafted comb-like vinyl or acrylate polymers are influenced by their long-chain backbones as observed in experiments. By means of dynamic Monte Carlo simulations of the lattice polymer model, we compared cooling and isothermal crystallization behaviors of side chains in bulk alternatingly grafted polymers separately holding crystallizable and non-crystallizable long-chain backbones. The results of a series of side-chain lengths showed that both non-crystallizable backbones and very short side chains suppress side-chain crystallization in agreement with experiments, demonstrating the constraint effects of the backbone on side-chain crystallization. However, both crystallizable and non-crystallizable long-chain backbones maintain their nearly random-coil conformation over side-chain crystallization, not adopting the expected bottle-brush shapes. We discussed the related experimental observations on crystal morphologies that derived the bottle-brush assumption. Our observations facilitate a better understanding of structure-property relationships for side-chain crystallization in densely grafted comb-like polymers holding relatively long backbones.

Poly(Lactic Acid) (PLA)-Based Nanocomposites: Impact of Vermiculite, Silver, and Graphene Oxide on Thermal Stability, Isothermal Crystallization, and Local Mechanical Behavior

The structural, thermal, and mechanical properties of unreinforced and reinforced polylactic acid (PLA) were investigated. The PLA was a biopolymer that was reinforced with four fillers (i.e., graphene oxide (GO) and silver (Ag); vermiculite (VMT) and silver (Ag); and two organically modified vermiculites). The processing technique for the production of the composite materials were carefully planned. The PLA nanocomposites were investigated by examining their morphological aspects, changes in PLA phases and transitions and, most importantly, the effect on certain final properties. X-ray diffraction and differential scanning calorimetry (DSC) analysis indicated that the sample was completely amorphous. Thermogravimetric analysis (TGA) results indicated that the presence of reinforcing particles in the PLA matrix did not affect the thermal degradation of these composites. Furthermore, the local mechanical properties were investigated using the microindentation method to evaluate the effect of different nanofillers. Scanning electron microscopy (SEM) and a VHX-500 optical digital microscope (Keyence International, Mechelen, Belgium) were also used to examine the surface morphology of the PLA polymer composites. These results can help to select suitable fillers to enhance the PLA performance of biopolymers.

Effects of microalloying on the isothermal and non-isothermal crystallization behaviors of TiZrSi-based metallic glasses

Effects of microalloying on the isothermal and non-isothermal crystallization behaviors of TiZrSi-based metallic glasses

Isothermal crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 in terms of crystal growth, overall volume crystallization kinetics and their relation to the viscosity temperature dependence

Abstract The crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 metallic alloy has been studied with the aid of differential scanning calorimetry, optical metallography, and electron microscopy methods. The crystallization occurs as a single-stage process starting preferably on the surface of casting voids in the sample volume and on the outer sample cutting planes. The linear crystal growth velocity of crystallizing cells was measured at several constant temperatures in the range 590 –620 K. It is constant at constant temperatures and its temperature dependence is in good agreement with the theoretical concepts of Uhlmann using the temperature dependence of the viscosity of the alloy studied. A differential scanning calorimetry study of isothermal overall volume transformation kinetics of samples pre-annealed at 600 K for 600 s was carried out at several constant temperatures. The experimental data are interpreted on the basis of the equation of Kolmogorov-Avrami-Johnson-Mehl for the case of three-dimensional growth of a fixed number of pre-existing nuclei. The possibility to revitrify the crystallized samples by their melting in differential scanning calorimeter, followed by quick cooling with cooling rate of 5 K τ– 1 is shown. The volume transformation kinetics of revitrified samples has been also studied.